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"Cannot open your default e-mail folder" error when users try to open their mailboxes in Outlook after migration to Exchange 2010

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After a migration from an earlier version of Microsoft Exchange Server to Microsoft Exchange Server 2010, users cannot connect to their mailboxes in Microsoft Outlook. Additionally, users receive the following error message:

Cannot open your default e-mail folder. Microsoft Exchange is not available. Either there are network problems or the Exchange computer is down for maintenance.

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This issue occurs because the user proxy address is stamped in two directory objects.

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To work around this issue, users can connect to their mailboxes by using Microsoft Outlook Web App (OWA).

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To resolve this issue, remove the duplicate proxy address in Active Directory Domain Services (AD DS). To do this, follow these steps:
  1. Log on to the Client Access server (CAS) to which the users are connected, and then locate the following folder that stores the log file: 
    C:\Program Files\Microsoft\Exchange Server\V14\Logging\RPC Client Access
  2. Open the RCA-YYYYMMDD-X.log file, and then search events that are related to the users in question. For example, you find the following information:

    /O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest' ,,,12.0.6315.5000,,,fe80::78dd:fc1:9cb8:2e72%11,ncacn_ip_tcp,Connect,0,,,RpcDispatch: Unable to map userDn '/O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest' to exchangePrincipal (StoreError=UnknownUser)
    '/O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest' ,,,12.0.6315.5000,,,fe80::78dd:fc1:9cb8:2e72%11,ncacn_ip_tcp,Connect,0,,,RpcDispatch: Unable to map userDn '/O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest' to exchangePrincipal (StoreError=UnknownUser)
  3. Copy the LegacyexchangeDn information of the user. For example, copy the following:

    /O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest
  4. In Active Directory Users and Computer (ADUC), right-click the domain object, and then click Find.
  5. Click the list next to Find, and then select Custom search.
  6. Click Advanced, type the following Lightweight Directory Access Protocol (LDAP) statement under Enter LDAP query, and then click Find Now:

    (proxyaddresses=X500:/O=Contoso/OU=First Administrative Group/cn=Recipients/cn=USERTest)C
  7. Determine whether any duplicate users are returned.
  8. Check the X500 address of any returned users, and then remove the duplicate proxy address for those users.
Note After you perform these steps, users can successfully connect to their mailboxes by using Outlook.

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More Information

To search duplicate proxy addresses in AD DS, you can also use one of the following LDAP statements:
  • (proxyaddresses=X400:C=US;A= ;P=Contoso;O=First Administrative Group;S=User;G=Test)
  • (
  • (
  • (proxyaddresses=X500:/o=Contoso/OU=First Administrative Group/CN=Recipients/CN=TestUser)

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Keywords: kb, vkbportal226, vkbportal250

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Article Info
Article ID : 2521770
Revision : 2
Created on : 11/15/2019
Published on : 11/15/2019
Exists online : False
Views : 118